Subsequent to early work on disc and drum files for data processing systems, usage of contact recording was generally dropped as air bearing magnetic heads and associated support mechanisms were developed for "flying" a transducer at a small spacing from a magnetic recording surface, to permit intimate interaction between the transducer and the magnetic surface. Contact recording continued to be used in magnetic tape systems, for which multi-channel heads were typically employed. However, contact recording for disc media was revived with the introduction of the so-called "floppy" disc system, in which a thin pliant disc element contained within a cover jacket was used in combination with low cost accessing, transducing and control systems. Floppy disc systems have subsequently found widespread application not only in the program storage and entry applications for which they were originally intended, but also in a wide variety of data entry, storage and control applications. In the original systems, and since that time, the transducer structure generally comprises a single channel head with associated erase head, mounted in a transducer having a contact surface that is a segment of a spheroid or at least curved, the transducer itself being mounted in a carriage element that is accessed to different circumferential tracks on the floppy disc. On the opposite side of the disc from the transducer, and also in contact with the disc, is a pressure pad mounted adjacent the end of a spring-loaded arm, which is solenoid controllable so as to be free to exert pressure when data transfer operations are to take place.
Recently, however, the floppy disc industry has started to use both sides of the floppy disc for data transfer operations, the purpose primarily being to increase capacity. Thus only a single relatively low speed accessing mechanism continues to be employed, and the transducers on opposite sides of the element are in a generally opposed relation, with only a slight offset in the head gaps to avoid flux interaction. Because it is thought necessary to account for perturbations in movement of the flexible disc from its principal plane, recording heads and mounts are utilized that are essentially derived from the flying head technology. Specifically, a pair of small, identical slider heads are used, each mounted adjacent the end of a long resilient cantilevered head support, and mechanically urged together with a total force of approximately 8 grams. The concept is that as the flexible disc deviates from its principal plane, both of the heads tend to follow the actual position of the disc passing between them and permit contact recording without excessive wear or signal degradation. Accepted industry standards for functional specifications are 1,000,000 revolutions without substantial degradation in reproduced signal amplitude, and 3,000,000 revolutions without significant head wear.
There are, however, significant problems and limitations arising from the use of this double, symmetrical and very compliant head mechanism. The resilient mounts are relatively complex and must be precisely manufactured, and therefore are costly to manufacture and maintain. Furthermore, they require redesign, by each floppy disc manufacturer, of the carriage, head support mechanisms and associated structure, becase they have volumetric configurations incompatible with current structures. In addition, the head loading force and the mechanical configuration require that special provision be made to insure that the head does not constantly land at the same point and thereby cause undue wear. In addition, the long flexible columns used in the existing type of structure tend to bend in a slight S shape or shift differentially in response to perturbations in the disc surface position. This introduces both a degree of offset relative to the track center, reducing reproduced signal amplitude and tending to limit the positional accuracy which can be obtained, which in turn limits the track density which can be achieved. Furthermore, the two resiliently mounted heads do not settle quickly into operative relation, once landed on the disc, and this delay must be taken into account before data transfer operations can begin. Of great importance from the standpoint of the floppy disc systems manufacturer is the fact that he not only cannot use a portion of his existing inventory for heads and carriages, but must redesign a portion of his system for the new double sided configuration.
There are currently recognized both distinctions and similarities between contact and non-contact recording. In non-contact recording the purpose is to employ an aerodynamic effect to fly the transducer at given spacing above the record medium. This distance is decreasing as the art advances and some current systems use a little as 10-20 microinches, but a primary objective is to avoid contact or "head crash" during rotation. In contact recording a film of air is actually interposed between the head and the record medium during operation, but this is typically only a few microinches. In contact recording frictional contact and wear are inherent, and the head design must accommodate these factors. It can be seen, however, that in operative use both types use an air bearing effect and that the distinction is growing less clear as non-contact types fly at smaller heights and floppy discs are driven faster.